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.nto which short, narrow glass tubes are inserted. Attach one
snd of the tube to an apparatus for evolving carbon dioxide,
ivhich is thoroughly dried by passing it through concentrated
sulphuric acid. When the air is expelled from the tube, heat it
gently until the alcohol is removed. Then let the tube cool
while the gas is passing through. The spiral is then removed
ind placed in the front of the combustion tube. The combustion
is carried out in the manner already described, but a current of
lir is substituted for oxygen until all the hydrogen has been
expelled, z>., until water ceases to condense in the front of the
:ube. The burners under the metallic copper are then gradually
2xtinquished, and the spiral allowed to cool whilst the current
D£ air is replaced by oxygen. By the time the oxygen reaches
:he spiral, the latter should have so far cooled that it remains
anoxidised. The current of oxygen is continued until a glowing
:hip is kindled at the end of the potash apparatus and the
operation is completed by turning on the air as previously
A convenient substance to use for analysis is acetanilide, see
Preparation 54, p. 151.
Combustion of Organic Compounds containing
Halogens and Sulphur.—When the halogens or sulphur
are present in an organic compound, they are liable to be ab-
sorbed either in the free state or in combination with oxygen in the
potash apparatus. In this case, fused lead chromate broken up
into small pieces must replace the coarse copper oxide in the
combustion tube. The halogens and sulphur are retained by the
lead, the former as the halide salt, and the latter as lead sulphate
Special care must be taken in using lead chromate, that the
temperature of the furnace is not too high, as otherwise the
chromate fuses to the glass, and the combustion tube then
cracks on cooling.
Nitrogen (Dumas).—According to this method, a weighed
quantity of the substance is heated with copper oxide in a tube
filled with carbon, dioxide. The carbon and hydrogen form
respectively carbon dioxide and water, and the nitrogen which
is liberated in the form of gas is collected over caustic potash
(which absorbs the carbon dioxide) and measured.
The following apparatus-is required :—
l. A combustion furnace of the ordinary form.